Free cutting steels

ABSTRACT

This invention relates to free-cutting carbon steels such as S20C steel, S30C steel, S45C and S55C steel as indicated by the Japanese Industrial Standards (or steel Nos. 1020 to 1055 as indicated by the SAE Standards) containing 0.20 to 0.56 percent carbon, 0.24 to 0.33 percent silicon and 0.35 to 0.78 percent manganese. Also, this invention relates to free-cutting Ni-Cr steels, Cr-Mo steels and Cr steels containing 0.29 to 0.42 percent carbon, 0.24 to 0.33 silicon, 0.51 to 0.75 percent manganese, 0.07 to 2.89 percent nickel, 0.76 to 1.14 percent chromium and 0 to 0.26 percent molybdenum. They are characterized by the oxide inclusion contained in them, and also the calcium content and the improved free-cutting characteristic.

I United States Patent [111 3,630,723

[72] Inventor Chiald Audit [56] References Cited WM P" UNITED TATE E [21] App]. No. 759,706 3 192 040 s S PAT NTS 6/1965 Goda 75/123 [22] Filed Sept. 13, 1968 3 323 9 l1 6/1967 lnoue 75/123 [45] Patented Dec. 28, 1971 3 468 638 9/1969 H ald [73] Assign M Seiko Kbuahlld Km er 75/123 Nagoya, Aicei Prefecture, Ja an Primary Examiner- Hyland Bizot [32] Priority Sept. 19, 1967 Att0rney-Wenderoth, Lind 8: Ponack [33] Japan [31] 42/59620 ABSTRACT: This invention relates to free-cutting carbon steels such as 820C steel, 830C steel, S45C and 855C steel as 54 FREE C G TEELS indicated by the Japanese Industrial Standards (or steel Nos. 2 Claims, 10 Drawlngl igs. 1020 to 1055 as indicated by the SAE Standards) containing 0.20 to 0.56 percent carbon, 0.24 to 0.33 percent silicon and Cl 75/128 R 3 3 0.35 to 0.78 percent manganese. Also, this invention relates to l Int Cl 37 0o free-cutting Ni-Cr steels, Cr-Mo steels and Cr steels contain- Fkld fseuch 75 ing 0.29 to 0.42 percent carbon, 0.24 to 0.33 silicon, 0.51 to l 1 0.75 percent manganese, 0.07 to 2.89 percent nickel, 0.76 to 1.14 percent chromium and 0 to 0.26 percent molybdenum. They are characterized by the oxide inclusion contained in them, and also the calcium content and the improved freecutting characteristic.

PATENTEU UEC28|97I 630. 723

sum 1 or 4 10 6 [07 A THE RECYCLED NUMBER g 300 SZOC-A ggoc- OF TESTS (N) F162 5 200 g I50 I- I00 L1) {5 INVENTOR MIDDLE BOTTOM CH'AKI DA BY MM ATTORNEYS PATENTEU UEC28 I971 SHEET 3 [IF 4 8 IO 20 3o 50 80100 LIFE OF TOOL( MINUTES) FIG 5 BIO . 2o 30 LIFE OF TOOL (MINUTES) FIG .6

SCM4-A RA 0 A S MA Mm M H C 0 E I.) m p P T N E T m M W m IMAM C I0 2 0 ATTORNEYS FREE CUTTING STEELS This invention relates to free-cutting steels which can easily be cut and which are obtained by controlling the oxide inclusion contained in certain steel. Particularly, this invention relates to free-cutting steels containing an oxide inclusion which consists of anorthite (CaO:Al,O -2SiO- as a principal component and having a calcium content of from 20 to 100 parts per million (20 to I p.p.m.

I-Ieretofore, a specific element such as P, N, Pb, Bi, S, Se or Ti is incorporated in the conventional free-cutting steels as a free-cutting component. In such free-cutting steels, the components such as P and N cause brittleness in the body of the steel and also a component such as Pb or Bi is crystallized in a different phase as fine crystals separate from the structure of the steels. Also, a component such as S, Se or Te is combined with other elemental components contained in the steel and forms the different phase in the structure of steel.

This invention, however, relates to free-cutting steels which are developed on the basis of the utilization of an oxide inclusion and therefore such free-cutting steels are different in their intinsic nature from the conventional free-cutting steels as mentioned above.

This invention is fully explained hereinafter by referring to the accompanying drawings in which:

FIG. 1 is a trigonometric diagram illustrating the distribution of the three components CaO, N 0 and SiO contained in the known free-cutting steel and the free-cutting steel of this invention.

FIG. 2 is a graph with curves illustrating the relationships between the strength fatigue and the number of cycles in the test when S45C-A steel, S45C-C steel and S45C-O steel were tested for fatigue. In FIG. 2, the horizontal axis indicates the number of cycles and the vertical axis indicates the stress amplitude. It is noted that S45C-A steel, was produced by treating S45C steel so as to have an A-type oxide inclusion and S45C-C steel was produced by treating 845C steel so as to have a C-type oxide inclusion as defined in the Japanese Industrial Standards. Also, it is noted that S45CO steel was not treated and so it is the same as 845C steel.

FIG. 3, is a graph with curves illustrating the relationship between the elongation, the reduction of area or the Charpy impact strength and the tensile strength when the above mentioned S45C-A steel and S45C-C steel were tested for their mechanical properties. The horizontal axis indicates the tensile strength and the vertical axis indicates the elongation, the reduction of area and the Charpy impact strength.

FIG. 4 is a graph with curves illustrating the relationship between the elongation, the reduction of area or the Charpy impact strength and the tensile strength when SCM3-A steel and SCM3-C were tested for their mechanical properties. It is noted that SCM3-A steel was produced by treating SCM3steel so as to have an A-type oxide inclusion and SCM3-C steel was produced by treating SCM3steel so as to have a C-type oxide inclusion as defined in the Japanese Industrial Standards. The horizontal axis indicates the tensile strength and the vertical axis indicates the elongation, the reduction of area and the Charpy impact strength.

FIG. 5 is a graph with curves illustrating the relationship between the cutting speed and the life the tool when SCA steel, SC-A steel, S45C-A steel, S55C-A steel, S20CC Steel, S30C-O Steel, S45C-O steel and S55CO steel were tested therefor. It is noted that the former four steels were produced by treating 820C steel, 530C steel, 545C steel and 855C steel so as to have an A-type oxide inclusion, and the latter four steels were not treated and therefore they are the same as 520C steel, 830C steel, 845C steel and 855C steel respectively. In FIG. 5 the vertical axis indicates the cutting speed and the horizontal axis indicates the life of the tools tested.

FIG. 6 is a graph with curves illustrating the relationship between the cutting speed and the life of the tools when SCr3- A steel, SCr4-A steel, SCM3-A steel, SCM4-A steel, SNC2-A steel, SCr3-O steel, SCr4-O steel, SCM3-O steel, SCM4-O steel and SNC2-O steel were tested therefor. It is noted that the former five steels were produced by treating SCr3 steel, SCr4 steel, SCM3steel, SCM4 steel and SNC2 steel so as to have an A-type oxide inclusion respectively. and the latter five steels were not treated and therefore they are the same as the steels indicated by SCr3, SCr4, SCM3, SCM4 and SNC2 respectively. In FIG. 6, the horizontal axis indicates the life of the tools tested and the vertical axis indicated the cutting speed.

FIG. 7 is bar graph showing the life of the tools comparing S20C-A steel with S20-C steel. It is noted that S20CC steel was produced by treating 520C steel so as to have a C-type oxide inclusion as defined in the Japanese Industrial Standards.

FIG. 8 is a graph with curves illustrating the relationship between the life of tools and the calcium content of S45C-A steel and SCM4-A steel. The life of tools is indicated by the vertical axis and the calcium content is indicated by the horizontal axis.

FIG. 9 is a photograph showing the status of the A-type inclusion contained in the free-cutting steel according to this invention and FIG. 10 is a photograph showing the status of the C-type oxide inclusion contained in the known free cutting steel.

Some free-cutting steels which were developed on the basis of the utilization of an oxide inclusion have been reported by H. Opity and others of the Aachen engineering college in West Germany Such free-cutting steels are illustrated in FIG. 1 and its is noted that they are melted so as to contain an oxide inclusion which consists of the components within an area around the line ficonnecting the 50 percent point b" on the CaO- SiO line with the 50 percent point d" on the CaO-Al o line, and particularly within the hatched area as indicated by the sign a and also that the oxide inclusion consists of gehlenite (2CaO-Al O SiO as a principal component and the oxide inclusion exists in the form of globular oxide or agglomerate which is referred to as a C-type oxide inclusion as stated hereinabove.

Also the free-cutting steels of this invention are illustrated by referring to FIG. 1 and it should be noted that they are melted so as to contain an oxide inclusion which consists of the components within the hatched area around the line 5? connecting the 50 percent point b" on the CaO-SiO line with the SOpercent point c" on the SiO -Al O line and also that the oxide inclusion consists of anorthite (CaO-AI O -2SiO as a principal component, and as an additional component tridymite (SiO mullite (3Al O -2SiO Pseudo-wollastonite (CaO-SiO or corundum (A1 0 This is the first essential feature of this invention. Also, it should be noted that the compositions of the free-cutting steels of this invention are controlled so as to have a calcium content ranging from 20 to ppm. This is the second essential feature of this invention.

The reasons why the free-cutting steels of this invention are characterized by the first essential featured are explained as follows.

As can be seen from the photograph of FIG. 9, the freecutting steel of this invention contains an oxide inclusion having the characteristic that it is elongated in the direction of rolling. The oxide inclusion is referred to as an A-type oxide inclusion as stated hereinbefore. Thus, it will be understood that the A-type oxide inclusion is distinguishable from the C- type oxide inclusion contained in the conventional free cutting steel as shown in the photograph of FIG. 10. The photograph of FIG. 10 shows that the C-type oxide inclusion having a size of about 4011. in diameter becomes a starting point for destroying the steel due to fatigue and decreasing impact strength of the steel and thus the C-type oxide inclusion is not desirable for the free-cutting steels. 0n the contrary, the A-type oxide inclusion does not cause such phenomena.

An inclusion of 545C steel was converted into the A-type oxide inclusion thereby to form S45C-A steel and also an inclusion of 845C steel was converted into the C-type oxide inclusion thereby to form S45C-C steel as shown in the follow- 3 4 ing table I. In table I, it is noted that S45C-O steel contained 545C steel and 555C steel having the chemical composition as an unconverted inclusion, and also that each of the steels has shown in the following table 4was converted into the A-type the chemical composition as indicated. The test samples of oxide inclusion thereby to form S20C-A steel, S30C-A steel, these steels were normalized and then they were tested for the S45C-A steel and S55C-A steel respectively. In table 4, it is fatigue strength by using a fatigue test machine by which the noted that SC-O steel, S30C-O steel, S45C-O steel and test samples are fatigued by the action of bending moment SSSCO steel correspond to 820C steel, 830C steel, 545C derived by rotating aweight. The test results are shown in FIG. steel and 555C steel respectively containing an unconverted 2. As is obvious from the curves as shown in FIG. 2, S45C-A inclusion. They were normalized and subjected to a cutting steel has a fatigue strength similar to the fatigue strength of test at a feed of 0.2 mm./rev., 2.0 mm. of depth of cut and a S45CO steel, but the fatigue strength of S45C-C steel is 10 frank wear width of V,,=0.3 mm. by using a P l0 tool which is reduced. made of a TiC type ultrahard steel containing TiC in an TABLE 1 Chemical components (percent) Mechanical properties Yield Tensile Elonga- Reduction point strength tion of urea Hardness Steels C Si Mn P S Ca (kg/mm?) (kg/mm?) (percent) (percent) (111;) S45C-A... 0.45 0.32 0.72 0.014 0.013 0.000 43.6 70.0 28.2 50.0 213 A11 inclusion is converted into an A-type oxide inclusion. S45C-C... 0.42 0.30 0.73 0. 019 0.009 0.0058 43.0 72.1 30.0 40.0 211 An ineluslon is converted into a C-type oxide inclusion. 8450-0.-. 0.45 0.32 0.75 0.019 0.015 Trace 43.3 74. 5 24.0 45.0 212 An inclusion is not converted.

NOTE.-850 C. X 2 hAc.

An inclusion of 845C steel having the chemical composition amount of about 28 percent. The test results are shown in FIG. as shown in the following table 2 was converted into the A- 5. type oxide inclusion thereby to form S45C-A steel and also an TABLE 4 inclusion of 845C steel having the chemical composition as chemical com oncnts 8mm shown in the following table 2 was converted into the C-type l oxide inclusion thereby to form S45 CC steel. The S45C-A Steels sign 0 Si M11 s steel and the S45CC steel were tested for their mechanical S200 022 031 0,50 0,021 (1010 0, 0060 l h w FIG, o 0.22 0.20 0.38 0. 013 0.012 0.0000 pmpemes Thetestrebu ts ares O n m 3 woe {A 0.20 0. 33 0. 63 0.010 0.020 0. 0052 o 0.32 0. 24 0.70 0.013 0.030 0. 0001 TABLE 2 {A 0. 42 0. 30 0. 73 0. 010 0. 000 0. 0053 o 0. 45 0. 32 0.75 0. 010 0.015 0. 0000 Chemical c p n p n 055C {A 0. 54 0. 20 0. 73 0. 014 0. 020 0. 0001 o 0. (,0 0,25 0.72 0. 014 0.030 0.0001 Steels C Si Mn 1 S Ca 35 Q30 73 0-019 11-009 0-0058 h po oxide As can be seen from FIG. 5, the life of the tool is improved Inc US 011. I s45o-o... 0. 40 0.33 0.67 0.011 0. 013 0. 0051 The C-type oxide i pamculfl'ly a cufimg Speed of 30 mete ncl nminute when the A-type incluslon-contaming steels are cut.

M .4 An inclusion contained in each Of SCI'3 5166 SC Slee],

An inclusion of SCM3 steel having the chemical composi- 4O SCM3 steel, SCM4 steel and SNC2 steel having the chemical tion as shown in the following table 3 was converted into the composition as shown in the following table 5 was nve A-type oxide inclusion thereby to form SCM3-A steel and also into the A-type oxide inclusion thereby to form SCr3-A steel, an inclusion of SCM3 steel having the chemical composition SCr4-A steel, SCM3-A steel. SCM4-A steel and SNC2-A steel as shown in the following table 3 was converted into the C respectively. In table 5 it is noted that SCr3-O steel, SCr4 O type oxide inclusion thereby to form SCM3-C steel. The teel, SCM3-O steel, SCM4-O steel and SNC2-O steel cor- SCM3-A steel and the SCM3-C steel were tested for their respond to SCr3 steel, SCr4 steel, SCM3 steel, SMC4 steel mechanical properties. The test resul r h n in FIG. 4. and SNC2 steel respectively contain an unconverted inclu- TABLE 3 Chemical components, percent Steels C Si M11 P S Cr Mo Ca SCM3-A 0.36 0.31 0. 75 0.014 0.014 1.04 0. 24 0.0051 An inclusion is converted into 0. A-type oxide inclusion. SCM3-C 0.37 0.28 0.72 0.010 0.000 1.12 0.27 0.0057 An inclusion is converted into a C-type oxide inclusion.

Asis obvious from the curves as shown in FIGS. 3and 4, the sion. They were normalized and subjected to a cutting test elongation, the reduction of area and the Charpy impact conducted in the same manner as mentioned above. The test strength of both the S45C-C steel and the SCM3-C steel are results are shown in FIG. 6.

TABLE 5 Chemical components, percent Steels Sign O Si M11 P S Ni so {A 0.36 0. 23 0. 71 0.014 0.012 0.07 0 0.34 0.24 0.73 0.012 0.000 0.08 so {A 0. 41 0.27 0. 00 0.016 0. 000 0.10 O 0.39 0.30 0.72 0.013 0.011 0.11 SCM3 {A 0. 36 0.31 0. 75 0.014 0. 014 0.12 0.24

0 0.35 0. 28 0.71 0.011 0. 011 0.00 1.01 0.22 0.0000 SCM4 {A 0.42 0. 20 0.74 0.015 0.012 0.00 0. 03 0.25 0.0057 0 0.41 0.30 0. 00 0. 011 0. 008 0.10 1.00 0. 23 0. 0003 SNC2 {A 0.30 0.20 0.51 0. 010 0. 012 2.87 0.70 0. 0004 0 0. 20 0.27 0. 0. 013 0. 011 2. 30 0.31 0. 0000 lowered as compared with those of the S45C-Asteel and the As can be seen from FIG. 6, the life of the tool is improved SCM3-A steel. and particularly at a cutting speed of above I00 meters per An inclusion contained in each of 820C steel, 830C steel, minute.

S20C-A steel and S20CC steel as given in the following table 6 were subjected to cutting tests under a feed of 0.168 mm./rev., 1.0 mm. of depth of cut, a frank wear width of V,,=0.3 mm. and a cutting speed of I50 m./min. by using the P 10 tool. The testsamples were made of the top, middle and bottom part of the body of each of the steels. The test results are shown in FIG. 7. As can be seen from FIG. 7 a longer life was obtained for the tool tested for S20CA steel as compared with the tool tested for S20CC steel.

TABLE 6 Chemical components, percent Steels s1 Mn P P Ca S20C-A 0. 20 0. 27 0. 35 0. 006 0. 016 0. 0078 The A-type oxide inclusion.

S20CC 0. 22 0. 28 0. 43 0. 015 0. 010 0. 0067 The C-type inclusion.

Next, the reasons why the free-cutting steels of this invention are characterized by the second essential feature are explained as follows.

The test steels such as S45C-A steel Nos. 1 to 12 and SCM4-A steel Nos. 41 to 47 as listed in the following table 7 were subjected to cutting tests under a feed of 0.20 mm./rev.,

TABLE 7 Chemical components, percent Stet-ls Nos. 0 Si Mn 1 S Cr Mo Ca S45O A 6 0.45 0. 33 0. 80 0. 019 0. 012 0. 0026 7 0. 45 0. 30 0. 71 0.016 0. 013 0.0030

SCM4-A 44 0. 38 0. 29 0. 74 0.014 0.011 0. 0048 45 0. 42 0. 26 0.72 0. 012 0. 011 0. 0054 As can be seen from FIG. 8, the life of the tool is lowered and is not satisfactory when S45C-A steel and SCM4-A steel contain calcium in an amount of below about p.p.m. or above about 100 p.p.m. Thus, it is understood that the calcium content of the freecutting' steels of this invention is an essential feature and the calcium content is required in the range var ing from 20 p.p.m. to 100 p.p.m.

he inventor has found that the A-type oxide inclusion contained in the free-cutting steels of this invention is softened or molten when said steels are cut with the cutting tool and that the tool was covered with the molten oxide inclusion and the tool is protected from wear. The typical S-containing freecutting steel, the Pb-containing free-cutting steel and the freecutting steel of this invention were compared with nonfreecutting steel by evaluating their shear strain on the cutting shear plane based on the effect of stress concentration in the inclusion and the frictional stress on the rake face of the tool based on the effect of less friction. The following table 8 shows the ratio of the shear strain on the cutting shear plane for the free-cutting steels to the shear strain on the cutting shear plane for the nonfree-cutting steel and also the ratio of the frictional stress on the rake face of the tool for the free-cutting steels to the frictional stress on the rake face of the tool for the nonfree-cutting steel.

it is obvious from the data as shown in table 8 that the freecutting characteristic of the free-cutting steels of this invention is not due to the effect of stress concentration in the oxide inclusion but due to less frictional stress on the rake face of the tool. Thus, it is necessary that the oxide inclusion be softened or molten depending on the cutting conditions of the free-cutting steels and it was found from measurement of the temperature on the rake face and observation of the layer adhered to the tool that the oxide inclusion contained in the f reecutting steels of this invention must have a melting point of from l,l00 C. to L550 C. and also that the melting point was determined by the oxide inclusion contained in the freecutting steels of this invention.

What] claim is that:

l. Free-cutting plain carbon steels consisting essentially of 0.2 to 0.5 percent carbon, 0.24 to 0.33 percent silicon and 0.35 to 0.78 percent manganese, said steels being characterized by an oxide inclusion comprising anorthite (CaO-AI O; -2SiO as a principal component and a calcium content ranging from 20 to p.p.m. and balance iron.

2. Free-cutting Ni-Cr, Cr-Mo and Cr-steels consisting essentially of 0.29 to 0.42 percent carbon 0.24 to 0.33 percent silicon, 0.5l to 0.75 percent manganese, 0.07 to 2.89 percent nickel, 0.76 to 1.14 percent chromium and 0 to 0.26 percent molybdenum, said steels being characterized by an oxide inclusion comprising anorthite (CaO-Al O -2SiO as a principal component and a calcium component ranging from 20 to I00 p.p.m. and balance iron.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIO PATENTNO.: 3,630,723

DATED 1 December 28, 1971 INVENTOR(S) I ASADA It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 47, change "0.5" to 0.56

Signed and Sealed this Fifteenth Day of May 1979 [SEAL] Attest:

DONALD w. BANNER RUTH c. MASON Attesting Oflker Commissioner of Pater: and Trademarks 

2. Free-cutting Ni-Cr, Cr-Mo and Cr-steels consisting essentially of 0.29 to 0.42 percent carbon 0.24 to 0.33 percent silicon, 0.51 to 0.75 percent manganese, 0.07 TO 2.89 percent nickel, 0.76 to 1.14 percent chromium and 0 to 0.26 percent molybdenum, said steels being characterized by an oxide inclusion comprising anorthite (CaO.Al2O3.2SiO2) as a principal component and a calcium component ranging from 20 to 100 p.p.m. and balance iron. 